1. Field of the Invention
The present invention relates to a semiconductor mirror-polished surface wafer whose front and rear surfaces can be distinguished. In particular, the present invention relates to a semiconductor mirror-polished surface wafer whose rear surface is acid-etched and a method for manufacturing the semiconductor mirror-polished surface wafers.
2. Description of the Prior Art
In an ordinary device manufacturing process, the rear surface of a semiconductor mirror-polished surface wafer is always sucked and held by a sucker and circuits are formed on the front surface. When, only the front surface of the semiconductor mirror-polished surface wafer is mirror-polished and the roughness of the rear surface remains unpolished, due to the suction force, the unevenness of the rear surface could transfer to the front surface. This will bring about a harmful effect to the device manufacturing process and lessen the yield of the device manufacturing process. Therefore, the both front and rear surfaces of a wafer are simultaneously or separately polished into mirror surfaces to avoid a decrease in the yield.
However, either surface of the two-sided mirror-polished surface wafer can not be distinguished from each other. In particular, in a manufacturing device provided with a sensor for detecting the front side and the rear side, an "error" sign appears if the sensor can not detect the rear side. Therefore, a semiconductor mirror-polished surface wafer, whose rear surface is nearly mirror-like and capable of being detected by the sensor, is required.
The method for manufacturing such a semiconductor mirror-polished surface wafer has been disclosed in, for example, Japanese Patent Laid-open No. 6-349795. In Japannese Patent Laid-open No. 6-349795, semiconductor mirror-polished surface wafers are alkali-etched, and then their rear surfaces are polished. The front surfaces are polished subsequent to the polishing of the rear surfaces. In the process of polishing the rear surfaces, the roughness of the rear surfaces brought about in the foregoing etching process is polished with a trivial amount being remained so as to enable the identification of the front surface and the rear surface. To maintain the flatness during manufacturing processes, the etching processes employed are limited to alkali etching processes.
However, problems other than flatness, induced during alkali etching processes, still exist; for example, particulate residue, dust and metal contamination.
Furthermore, in order to remove pits or control the glossiness of the wafers, the rear surfaces have to be polished. The time spent in polishing the rear surfaces would lessen the productivity.